According to Pennsylvania law, can you record someone without their knowledge?

Federal law [18 U. S. C. 2511(2)(d)] provides for "one-party consent" to record conversations; you can be the consenting party. Some states (not Pa. ) prohibit recording conversations without permission of all parties. The location of the other party is an issue of s/he is in a state that prohibits recording. What you can do with the recording then is a separate matter.

Under any states law you would be very ill-advised to do this. The only individual that can be recorded without their consent is a child at birth, by legal parents or designees. Doing otherwise is fraudulent and a heads-up to authorities that you may be considering felony abuse, fraud, or theft of property.